c hapter 4 computer networks. chapter 4 a computer network is a collection of computers and devices...
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CHAPTER 4
Computer Networks
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Chapter 4• A computer network is a collection of computers and devices
connected by communications channels that facilitate communication and sharing of resources among users.
• They may be classified according to a wide variety of characteristics.
4.1 Local Area Network (LAN)• It is a combination of programs and equipment that connect a
number of personal computers. • It serves a local area. • Supplies networking capability to a group of computers in close
proximity to each other such as in an office building, a school or a home.
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4.1 Local Area Network (LAN)• Feasible for the owning organization to install high quality, high-
speed communication links interconnecting nodes. • Typical data transmission speeds are one to 100 megabits per
second. • Useful for sharing resources like files, printers, games or other
applications. • A LAN, in turn, often connects to other LANs and to the Internet
or other WAN.• Specialized operating system software may be used to configure a
local area network.
Examples: industrial plants, office buildings, college or university campuses or similar locations.
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4.1 Local Area Network (LAN)Ethernet LAN• The smallest home LAN can have precisely two
computers; a large LAN can accommodate many thousands of computers.
• Many LANs are divided into logical groups called subnets.
• It sets up the predictable and inevitable conflict between PCs, office automation equipment and the larger midrange and mainframe computers.
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4.1 Local Area Network (LAN)
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4.1.1 LAN TOPOLOGIES• Selecting the topology of the LAN is to
interconnect PCs, minicomputers, or both. • This choice dictates the cable, cabling
methodology and the networking software that can operate on the LAN.
• The three basic topologies are the ring, the star and the bus or tree.
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4.1.1 LAN TOPOLOGIES
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4.1.2 Linear Bus Topology
Consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable.
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4.1.2 Linear Bus TopologyA- Advantages of a Linear Bus Topology • Easy to connect a computer or peripheral to a linear bus. • Requires less cable length than a star topology.
B- Disadvantages of a Linear Bus Topology • Entire network shuts down if there is a break in the main
cable. • Terminators are required at both ends of the backbone cable. • Difficult to identify the problem if the entire network shuts
down. • Not meant to be used as a stand-alone solution in a large
building.
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4.1.3 Star Topology• Designed with each node (file server, workstations,
and peripherals) connected directly to a central network hub, switch, or concentrator.
• Data on a star network passes through the hub, switch, or concentrator before continuing to its destination.
• The hub, switch, or concentrator manages and controls all functions of the network.
It also acts as a repeater for the data flow. Common with twisted pair cable. Can also be used with coaxial cable or fiber optic cable.
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4.1.3 Star Topology
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4.1.3 Star Topologya- Advantages of a Star Topology • Easy to install and wire. • No disruptions to the network when connecting or removing
devices. • Easy to detect faults and to remove parts.
b-Disadvantages of a Star Topology • Requires more cable length than a linear topology. • If the hub, switch, or concentrator fails, nodes attached are
disabled. • More expensive than linear bus topologies because of the
cost of the hubs, etc.
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4.1.4 Tree or Expanded StarIt combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. They allow for the expansion of an existing network.They enable schools to configure a network to meet their needs.
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4.1.4 Tree or Expanded Star
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a- Advantages of a Tree Topology • Point-to-point wiring for individual segments. • Supported by several hardware and software venders. b-Disadvantages of a Tree Topology • Overall length of each segment is limited by the type of cabling used. • If the backbone line breaks, the entire segment goes down.
Star and ring network topologies are sometimes combined into one network to provide a higher degree of fault tolerance. Because a star network is susceptible to a failure in the hub and a ring network is sensitive to a break in the ring, combining both forms offer an alternate route in case one topology fails.
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4.2 Wide Area Network (WAN)
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4.2 Wide Area Network (WAN)• It is a collection of LANs. • It spans a large geographic area, such as a state, a province
or a country. • WANs often connect multiple smaller networks, such as
local area networks (LANs) or metro area networks (MANs).
• Many WANs are corporate or research networks that utilize leased lines.
• Wide Area Network (WAN) is a computer network that covers a broad area (i.e. any network, whose communications links cross metropolitan, regional, or national boundaries).